Module Name: src
Committed By: rillig
Date: Sat Apr 22 19:45:04 UTC 2023
Modified Files:
src/tests/usr.bin/xlint/lint1: msg_135.c
Log Message:
tests/lint: test cast to union with stricter alignment
To generate a diff of this commit:
cvs rdiff -u -r1.12 -r1.13 src/tests/usr.bin/xlint/lint1/msg_135.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/tests/usr.bin/xlint/lint1/msg_135.c
diff -u src/tests/usr.bin/xlint/lint1/msg_135.c:1.12 src/tests/usr.bin/xlint/lint1/msg_135.c:1.13
--- src/tests/usr.bin/xlint/lint1/msg_135.c:1.12 Tue Mar 28 14:44:34 2023
+++ src/tests/usr.bin/xlint/lint1/msg_135.c Sat Apr 22 19:45:04 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: msg_135.c,v 1.12 2023/03/28 14:44:34 rillig Exp $ */
+/* $NetBSD: msg_135.c,v 1.13 2023/04/22 19:45:04 rillig Exp $ */
# 3 "msg_135.c"
// Test for message: converting '%s' to '%s' increases alignment from %u to %u [135]
@@ -22,7 +22,7 @@ read_uint(const unsigned short **pp)
struct incomplete;
struct complete {
- int member;
+ int member;
};
/*
@@ -74,3 +74,30 @@ plain_char_to_unsigned_type(char *cp)
usp = (unsigned short *)cp;
sink(usp);
}
+
+/*
+ * Converting a pointer with a low alignment requirement to a union that
+ * includes other types with higher alignment requirements is safe. While
+ * accessing any other member of the union might trigger an alignment
+ * violation, such an access would invoke undefined behavior anyway.
+ *
+ * A practical case for this pattern are tagged unions, in which the first
+ * member of the struct determines how the remaining members are interpreted.
+ * See sbin/newfs_udf, function udf_validate_tag_and_crc_sums for an example.
+ */
+double
+cast_to_union(void)
+{
+ int align_4 = 0;
+ double align_8 = 0.0;
+ union both {
+ int p_align_4;
+ double p_align_8;
+ } *both;
+
+ /* TODO: don't warn here. */
+ /* expect+1: warning: converting 'pointer to int' to 'pointer to union both' increases alignment from 4 to 8 [135] */
+ both = (union both *)&align_4;
+ both = (union both *)&align_8;
+ return both->p_align_8;
+}
